The initial searches for ‘fits’ were done using tabulating machines which picked up coincidental streams of four or more letters, Mahon said. ‘At the same time messages were punched by hand onto Banburies, long strips of paper with alphabets printed vertically, so that any two messages could be compared together and the number of repeats be recorded by counting the number of holes showing through both Banburies.’
The Banbury sheets were about ten inches wide and several feet long. They had columns of alphabets printed vertically on them, giving horizontal lines of As, Bs, Cs, etc. Clerks punched holes into the paper to correspond with the encyphered messages, thus with a message beginning JKFTU, the J of the first column would be punched out, the K in the second column, the F in the third column and so on. They then aligned the sheets of paper over each other on top of a dark-coloured table and moved them to the left or right looking for repeats where the holes coincided and the table showed through.
The aim was to find points in a number of messages where a sequence of the machine coincided. If there were two messages with the indicators equating, for example, to the starting points XYK and XYM, then the second message would start two spaces on. So if the initial letter of the second message was moved to a position over the third letter of the first message then the letters in each column would be encoded in the same position. This would show up in an unusual number of repeats. The more repeats there were the more likelihood there was of the two sequences having been encyphered in the same position.
‘If you’re lucky and you’re lucky pretty frequently, you might come across a four-or five-letter repeat,’ said Peter Twinn.
You would say to yourself, ‘A five-letter repeat, it’s greatly against the odds, there must be a reason for it, what is it?’ and the answer is that it represents the re-encodement of the same German word in both messages and you might be able to make a reasonable guess at what it was, having seen some German messages encyphered in the past. So that would give you a little start and then you would try and fit a third message on and you might find with a bit of luck that, when you staggered it off with both of them, this third message had two trigrams. One clicked with one of your messages and another trigram clicked with three in a quite different place on the first message. I’m leaving out a lot of the difficulties, but you gradually build up a selection of twelve or fifteen messages out of the day’s traffic which if you make some other guesses and, if you’re very, very lucky, you can do one of a number of three things. You can, for a start, cut down the number of wheel orders the Bombes need to check. But you can also either find out the wiring of a brand new wheel or you can work out with a reasonable degree of accuracy what these messages might be saying.
The Hollerith tabulating machines, mechanical digital data processors, which made the initial searches for the Banburismus ‘fits’, were provided by the British Tabulating Machine Company (BTM) based at Letchworth. They were controlled by a BTM expert called Frederic Freeborn, who ran the central index in Hut 7, which initially housed the automated Hollerith punch-card sorters. Under Freeborn’s direction, female clerks not only carried out searches of the Enigma traffic for features that might assist the codebreakers, they cross-referenced every piece of information passing through Bletchley onto punch cards. A request for details of a radio station, unit, codeword, covername or indeed any type of activity would swiftly produce every card containing any previous mention or occurrence.
Marjorie Halcrow, a 22-year-old graduate from Aberdeen University, was one of those recruited by Freeborn to work in Hut 7. ‘The cards were actually punched up on a machine about the size of a typewriter,’ she said.
There was a room containing about twenty or thirty of them called the punch room where girls copied the coded messages onto these punch cards. The main room contained much larger machines, about the size of a small piano, called the sorting machines which could read the cards and sort the hundreds of thousands of messages into different categories. There were loads of sorters and there were collating machines that were even larger. The whole department was filled with machinery. It was a very noisy place, all banging on all night and day long.
Eventually there were so many Hollerith machines in use that they were operated at four separate outstations clustered around Bletchley. This frequently forgotten part of Britain’s wartime codebreaking operations was not always used as efficiently as it might have been. Welchman recalled:
The cryptanalytical sections would have had a better service if they had simply discussed their needs with Freeborn instead of dictating to him. This would have given him the chance to programme the overall use of his equipment and staff in a way that would have been advantageous not only for each individual problem solution, but for the overall service he was providing.
Hut 8 was now divided into four sections. The registration room, where the traffic arrived and was sorted; the ‘Banburismus Room’, where codebreakers tried to break the keys using Banburismus; the ‘Crib Room’, where the codebreakers tried out cribs; and ‘the Big Room’ where female clerks punched up the messages on the Banbury sheets and decyphered messages on Type-X machines once the wheel order, settings and keys had been recovered.
The codebreakers themselves rarely read the decrypts. Peter Twinn recalled having very little interest in what they were actually saying. ‘I would have to confess I don’t think I really understood the full significance of it,’ he said.
I think I’d have to excuse myself by saying that we lived at that time in a very narrow little world. Remember that I was an inexperienced lad of twenty-four or twenty-five and I’d come into it straight from university, I don’t think I had a real grasp of what a major war was all about and we did work very much in a rather monastical way. I don’t recall ever having decoded a message from start to finish to see what it said. I was much more interested in the methodology for getting German out of a coded message.
The decyphered messages were passed via Z Watch, the Naval Section’s equivalent of Hut 3, over a newly installed teleprinter link that allowed the Hut 8 decrypts to be sent direct to the OIC, giving prior warning of the wolf-pack patrol lines and allowing the convoys to be routed away from danger. The OIC was fully indoctrinated into Enigma so there was no need for the agent’s disguise required for Hut 6 German Army and Luftwaffe decrypts. The result was truly dramatic. Between March and June 1941, the U-Boats had sunk 282,000 tons of shipping a month. From July, the figure dropped to 120,000 tons a month and by November, when the wolf packs were temporarily withdrawn from the Atlantic, to 62,000 tons.
The breaking of the Naval Enigma was one of the main reasons for this drop in the fortunes of the U-Boats, providing the British with a welcome respite during which the vital supplies had a much greater chance of getting through, Harry Hinsley said.
It has been calculated that, allowing for the increased number of U-Boats at sea, about one-and-a-half million tons of shipping (350) ships were saved. This intermission was invaluable for the level of British supplies, the building of new shipping and the development of anti-submarine defences.
Despite the brilliance of men like Turing and Alexander, the Naval Enigma could not have been broken without the Bombes. Larger improved versions known as Jumbos because of their size had been introduced and in order to protect them from German air raids they were dispersed to new outstations at nearby Wavendon and Adstock. At the same time, the Bletchley Bombes were moved out of the back room in Hut 1 and into Hut 11, acquiring a number of new operators.
The eight Wrens who arrived on 24 March 1941 were a trial measure. Previously the Bombes had been operated by soldiers, airmen and sailors who before being called up had worked for BTM, which built the Bombes. But male servicemen were at a premium and the number of Bombes was being constantly increased to cope with the need to keep the breaks of keys going, so it was decided to try the Wrens out as ‘an experiment’.
Morag Maclennan had followed her brother into the Royal Navy at the age of sevent
een and was very disappointed to discover that she was being sent to Bletchley rather than Portsmouth or Plymouth.
We got off at the station and somebody met us and we went up a little gravel path, straight into Hut 11. There were all these machines and you were given a thing called a menu with this strange pattern of letters and figures on it. You had to plait up this machine at the back with these great big leads which had to be plugged into different bits.
Then at the front, you had this rack with rows and rows of drums marked up by colour and you were told what combination of colours you were to put on. You would set them all, press a button and the whole row went round once and then moved the next one on. It took about fifteen minutes for the whole run, stopping at different times, and you recorded the stop and phoned it through and, with any luck, sometimes it was the right one and the code was broken.
It was very smelly with the machine oil and really quite noisy. The machine kept clanking around and unless you were very lucky your eight-hour watch would not necessarily produce a good stop that broke a code. Sometimes you might have a good day and two of the jobs you were working on would break a code and that was a great feeling, particularly if it was a naval code. Obviously, we hoped to do it for everybody. But there was an extra little surge of pride if it was a navy one.
Initially, the Wrens were not trusted with any details of what they were doing and it was a boring, frustrating task, she said.
The job itself was pretty dull. You were just working the machines the entire time. Because if all the bread and butter codes were broken, there were always ones that had got missed from a few days before or trying out more experimental ones. So the Bombes were never idle. But after a bit I think it was thought that it would be useful for our morale to know a little bit more of what the codes were dealing with, what areas they covered and of course the odd successes. Some weren’t all that dramatic. They weren’t necessarily operational, but they were building up the picture of exactly what air force squadrons and tank units were where, or where ships were and what they were doing. But when we were breaking the U-Boat ones in particular, we were told about the U-Boat sinkings and convoy protection, so we felt good about that.
By the end of the war, there were just under 2,000 Bombe operators, of whom 1,676 were Wrens, at six different locations around the country. They had their own unit, HMS Pembroke V, and Wrens had gone on to take up a number of other roles in GC&CS, including codebreaking itself. They were billeted together at a number of beautiful old country homes, including Woburn Abbey, which became known as the Wrenneries. But they never allowed themselves to forget that they were part of the Royal Navy, calling their living quarters, fo’c’sles; their dormitories, cabins; and saluting the areas in front of the country houses in which they were billeted as the quarterdeck.
Their arrival improved the social life and the Wrenneries became renowned for their dances. Barbara Quirk lived in a Tudor mansion called Crawley Grange, an hour’s drive away from Bletchley.
I remember our watch was having a dance in the most glorious ballroom in Crawley Grange, beautiful oak panelling from floor to ceiling, and we were told by our chief officer, who didn’t work at Bletchley, that we couldn’t have any drink. So we got some of the men who were coming from one of the camps around, they might have been Americans, they might have been British, I can’t remember now, to bring some beer. They brought a mobile bar on a jeep and parked it outside the Wrennery and when the chief officer found out, we were all gated for a month.
Joan Baily was billeted first at Crawley Grange and then at Gayhurst Manor, although she actually worked at Bletchley itself.
I found the atmosphere rather exciting because we had to try to break these codes and if we didn’t get the codes up we knew that somebody had had it. If we were on night shift, we had to sleep during the day of course and I remember they had problems with an RAF aircraft flying low over Gayhurst. We found out afterwards it happened to be because my sister was sunbathing on the roof with nothing on.
CHAPTER 6
A CRIME WITHOUT A NAME
The early spring of 1941 saw the German and Italian advance into the Balkans, a move that had been predicted by Bletchley on the basis of Luftwaffe preparations showing up in the Red Enigma and the heavy movement of German troops and armour south by rail which was reflected in messages encyphered on the German Railway Enigma. It was codenamed Rocket by Bletchley and broken by John Tiltman, who had a roving brief, breaking any codes and cyphers that were not being attacked, or could not be broken, by other departments.
Tiltman, the head of Hut 5, the GC&CS Military Section, was arguably one of the best codebreakers working during this period. Born in London on 25 May 1894, he was so obviously brilliant as a child that he was offered a place at Oxford at the remarkably young age of thirteen. He served with the King’s Own Scottish Borderers in France during the First World War, winning the Military Cross for bravery, and was seconded to MI1b, the War Office codebreaking unit, shortly before it merged with Room 40 to become GC&CS. A tall, rangy man, who had bad back problems and therefore liked to work standing up at a specially constructed high desk, Tiltman was a leading expert on hand cyphers. He habitually wore his regimental tartan trews, but had an otherwise rather casual approach to military uniform.
William Filby, who worked as a cryptanalyst in Hut 5, recalled their first meeting. ‘My arrival was unforgettable,’ Filby said.
As I saluted, I stamped the wooden floor in my Army boots and came to attention with another shattering noise. Tiltman turned, looked at my feet, and exclaimed: ‘I say old boy. Must you wear those damned boots?’ I became the only other rank at BP in battledress and white running shoes, much to the disgust of the adjutant.
Hut 6 was by now a much larger operation and it began to expand on the number of different Enigma cyphers it was working on. The reliance on the Red and the Brown Enigmas might well mean they were missing vital life-saving and war-winning intelligence. It also left the codebreakers vulnerable to German security improvements on the Luftwaffe keys. ‘All through this year [1941], there persisted, at any rate in my mind, the sensation that it was all much too good to be true,’ said Stuart Milner-Barry,
that any day now the enemy would discover, and that we should wake up one morning to discover, that it was all over. In those days the effects of getting in a jam were much more noticeable because with only two or three keys work simply came to a standstill if nothing broke for a few days and the whole Hut descended rapidly into the darkest abyss of despair.
Welchman, the head of Hut 6, expressed concern that Hut 6’s concentration on the Red Enigma was putting too many eggs in one basket. In a ‘screed’ to the members of Hut 6, he said,
Since we have neither enough intercept sets to cover all E [Enigma] traffic nor enough bombes to deal with all menus that could be produced we must be very careful to use our resources to the best advantage. Although we must concentrate the greater part of our resources on those colours which are high in the scale, it is most important that we ourselves should not lose interest in any type of E traffic. We should retain a clear idea of what is worth doing, even if we cannot at present do as much as we would wish, and our aim should always be to break every key and to take all steps that may possibly assist future breaking. From the crytographic point of view the breaking of any key may be valuable because key repeats or re-encodements may occur.
Hut 6 broke into Violet, the Luftwaffe administrative cypher, on Christmas Eve 1940 and Light Blue, the Luftwaffe cypher for north Africa and the Mediterranean, on the last day of February 1941, an event that led to raucous celebrations. ‘This occurred when the first party of American visitors were being shown round Hut 6,’ recalled Stuart Milner-Barry, ‘and must greatly have astonished any of them who had the idea that the British were a phlegmatic race.’
A lack of MI6 coverage of Italy, highlighted in 1935 by the Abyssinia Crisis and caused in part by the refusal of the British ambassador in Switzerland
to allow MI6 to use Switzerland as a base for running agents into Italy and in part by lack of funding, led the then Chief of MI6 Admiral Hugh Sinclair to rely heavily on GC&CS to produce intelligence on Italy. As a result, Bletchley Park had good coverage of Italian codes and cyphers and was able to warn of Italy’s entry into the war in June 1940, a month ahead of time. Italian diplomatic and colonial cyphers had been read for several years and the Naval Intelligence Italian section, led by William ‘Nobby’ Clarke, was completely on top of most Italian naval codes and hand cyphers from about 1937 onwards. Similarly, Bletchley was able to read most Italian air force and Army codes and hand cyphers. The Italian Enigma had been initially broken by Dilly Knox during the Spanish Civil War and was covered by his research section. It was unclear whether it was the same machine until, in September 1940, Mavis Lever, one of Knox’s assistants and only nineteen, managed to break the keys proving it was the same machine. She was halfway through a German degree at University College London when the war broke out.
I was concentrating on German romantics and then I realised the German romantics would soon be overhead and I thought well, I really ought to do something better for the war effort. I said I’d train as a nurse and their response was: ‘Oh no you don’t. You use your German.’ So I thought, great. This is going to be an interesting job, Mata Hari, seducing Prussian officers. But I don’t think either my legs or my German were good enough because they sent me to GC&CS.
She initially worked in a section in London perusing the personal columns of The Times for coded spy messages and using captured codebooks to decode them when Bletchley began to call for more staff.
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